의 안정도 Studies on the Synthesis and Structure Of
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DAEHAN HWAHAK HWOEJEE (J反e요 of the Korean Chemical Society) Vol. 31t No. 5, 1987 Printed in the Republic of Korea 전이금속 착물들의 합성 및 결정구조 연구 (제 1 보 ) EDTA 와 IMDA 복합 킬레이트가 란탄족 원소들 (La,Nd,Gd,Ho,Yb)의 안정도 상수에 미치는 영향 河英通t •金恩淵•崔圭源•金夏舆 서울대학교 자연과학대학 화학과 (1987. 5. 18 접수) Studies on the Synthesis and Structure of Macrocylic Complexes for Transition Metals. (Part 1) Effects of Stabili切 Constant on the Co-fonnation of Mixed Chelates (EDTA and IMDA) with Lanthanon (La, Nd, Gd, Ho, Yb) Young-Gu Ha\ E. Y. Kim, Q. Won Choi, and Hasuck Kim Department of Chemistry, College of Natural Sciences, Seoul National University^ Seoul 151, Korea (Received May, 18, 1987) 요 약. Ln-EDTA 1 : 1 착물과 IMDA 사이의 착물형성에 대한 안정도 상수들을 이온세기 “=0. IM, KNQ와 20.0士0.2°C 에서 전위차 적정법으로 연구하였다. Ln(EDTA) (IMDA) 혼합리간드착 물들에 비교적 큰 안정도 상수가 형성된다는 사실을 밝혔으며, Ln원소들의 원자번호에 대한 형성도 상수들의 경향을 Ln원소의 배위수와 반지름의 바탕에서 고찰하였다. ABSTRACT. The formation constants of the complexes between Ln-EDTA 1 : 1 complex and IMDA have been investigated by a potentiometric titration method at 20.0±0.2 degree C and “= 0.1 (KNO3). Unusually large stability in Ln (EDTA) mixed ligand complexes was found. Trends in the formation constants vs. atomic number of the lanthanide metals were discussed on the basis of coordination number and ionic radius of the metals. (earth) mixture. There are not rare elements, INTRODUCTION and the absolute abudance in the lithosphere is Lanthanide chemistry is initiated from the relatively high. discovery of an unusual mineral specimen ytterie Lanthanides are, strictly, the fourteen ele by Carl Axel Arrhenius in 1787 and of a mine ments that follow lanthanum in Periodic Table cerite by Axel Fredrik Cronstedt in 1751. and the fourteen 4f electrons are successively The lanthanides or lanthanoids except Pm, added to the lanthanum configuration. were originally known as rare earths from Since these 4f electrons are relatively uninvol their occurrence in phosphate rocks and oxide ved in bonding, lanthanides can be usually high —434 — 전이금속 착물들의 합성 및 결정구조 연구 435 Table 1. The properties of lanthanide, copper and zinc atoms and ions Electronic Configuration Atomic number Name Symbol E°(V) Ionic Radius Atom Ion Lanthanum 57 5d 6s2 -2.37 1.061A Neodymium 60 4f46s2 -2. 32 0. 995A Gadolinium 64 4f75d6s2 -2.29 0. 938A 67 H이 mium 4flx6s2 -2.33 0.894A 70 Ytterbium 4f146s2 -2. 22 0.858A Copper 29 3d10 4s +0. 337 87 pm Zinc 30 3d104s2 -0. 762 88pm Electronic configurations given above are only the valence shell electrons, that is, outside the (xe) shell for lanthan너e and (Ar) shell for lantharHde and (Ar) shell for Cu and Zn. Ionic state is +3 for Ln and +2 for Cu and Zn. E°(V) is Mn+ + ne_ —M. Here n—3 for Ln, n—2 for Cu and Zn. electropositive ions. The radii of these ions of sublimation of the metals, and lattice ener decrease with the increasing atomic number from gies, etc. lanthanum, thus constituting the lanthanide The absence of extensive ligand interaction contraction1. [Table 1) with the 4f orbital minimzes ligand field sta The cause of this contraction is that the bilization effects (LFSE) because lanthanides shielding of one 4f electron by another one. It behave as typical hard acids. The lack of LFSE is very imperfect because of the shapes of the reduces overall stability but, on the other hand, orbitals, the effective nuclear charge experienced provides a greater flexibility in geometry and by each 4f electron increases in each case. Thus this effect causes a reduction in size of the entire 4f shell2. But 4f orbitals are very effecti vely shielded due to the influence of external forces by the overlying 5s2 and 5p6 shells. Hence there are only slightly affected by the surroundings and remain practically invariant for a given ion in all compound. Oxidation state of lanthanides are usually tripositive because the sum of the first three ionization enthalphies is comparatively low. However, in aquous solutions - and in solids, quadripositive ionic cerium can be obtained and dipositive ionic samarium, europium, ytterbium, and thulium are also found. In solution, some dipositive ionic elements are oxidized readily to tripositive ionic states3. The existence of these Fig. 1. Partial molal volume of hydrated Ln3+. Lines various oxidation states can be interpreted by represent 9- and 8- coordination. Sm하 and Gd하 exist consideration of ionization enth시pies, enthalpies as equilibria between the two species. Vol. 31, No 5, 1987 436 河英鱼•金恩淵・崔圭源-金夏貞 Table 2. Colors and term symbols of electronic ground in the stability of the chelates formed with Ln states of the Ln3+ ions. and LN' alter separation factor more favorable Ion C이이 • Term symol 9, io Stabilities of lanthanide complexes are usually La3+ Colorless is。 Nd3+ Lilic 叮9/2 influenced by ionic radius of lanthanide, coor Gd3+ Colorless 料/2 dination number of its cation and coordinating Ho라 Pink: yellow 5i8 abilities of various donor atoms. In general Yb과 Colorless 2Ft/2 case, they are influenced by combination of above factors11- coordination number since LFSE is not lost4. Most of the studies on lanthanide complexes It is believed that coordination number of lan were purposed to separation. But nowadays, studies on coordination number of lanthanide thanides is larger than 6. Commo시y accepted coordination numbers of lanthanides are 7, 8, complexes are increased significantly7, n, 32. or 9s. It was suggested that coordination number Various investigators have determined the of lanthanide is 8 or 9. And Sm3+, Eu3+ or formation constant of lanthanide complexes by a potentiometric pH titration method 德이匕 Gd허' is transitional in coordination type6*7. potentiometric pH and pM titration method15,16, 1) The spin-orbit couping constants of the 4fn polarographic method17, spectroscopic methed18, electrons are so quite large (order of 1000cm-1), and proton magnetic resonance spectroscopic me as the lanthanide ions have ground states with thod33, etc. a single well-defined value of the total angular In recent years, the formation of lanthanide momentum. The colors and term symbols of complexes containing two different ligands has ele안ronic ground states of the Ln3+ ions are become of interest to coordination chemists, and the coordination numbers and geometries of these given in Table 2. Their geometries are monocapped trigonal complexes have been studied on the basis of the prism and monocapped octahedron at 7, square formation constant19^21. antiprism and dodecahedron at 8, and tricapped The tripositive lanthanide ions are well known trigonal prism at 91,8- to form hig이y stable 1 : 1 complexes Ln However, there are some di 伍 culities to (EDTA) - with ethylenediamine-tetraacetate separate these lanthaidde ions each other. The (EDTA4) origin of these di伍culties lies on the ubiqui — O^C — (가彳2\ /CH2 — CO2 — tousness of the tripositive state and the。시y >n-ch2-ch2-n< 一 O2C— 、 一 slight differences of the degree which a given ch/ CH2-CO2 (EDTA) property changes from ion to ion in this oxidation state. And the stability constants of these complexes Ion exchange is one of the separation me have been determined by a number of authors22. thods. In as much as the a伍nity of the two Since it was known that coordination number ions Ln and Ln' for the resin sites does not of Ln3+ ions is larger than six, on coordination differ markedly, elution by a simple cation is with the hexadentate EDTA, there is a possi not e任ective in achieving separation. But, if a bility that in the presence of the second ligand, suitable complexing agent is added, differences mixed complexes will be formed. Journal of the Korean Chemical Society 건이금속 착물들의 합성 및 결정구조 연구 437 In this study, formation constants between solutions were then filtered to remove undisso 1 : 1 complex of Ln (EDTA)- and iminodiacetate lved materials24. (IMDA) as the second ligand were determined Aliquots of each of these solutions were and the results were discussed on the basis of analyed for lanthanide metal content by oxalate coordination number of the lanthanide metals. precipitation and ignition at about 950 degree C. /CH2—CO2— HN< The lanthanide o^iddes which were supplied xCH2-CO2- by the lanthanide separation group at the (IMDA) Department of Chemistry, Seoul National Uni Cu2+ and Zn호 4' which have coordination versity were 99.9 % pure or better, and G. R. number less than six were also studied to com grade of nitric acid was used25. pare with Ln허 (b) Ligand Buffer solutions. Iminodiacetic acid (IMDA) was obtained from Aldrich Che EXPERIMENTAL mical Company, Inc., and G. R. grade acid (i) Apparatus form ethylenediaminetraacetic acid (EDTA, H4Y) The apparatus was consisted of titration cell was obtained from the Fisher Chemical Com with water jacket, a constant temperature bath, pany. They were dried for 3 hours at about 100 and a pump to citculate the water to maintain degree C and used without further purification. 20.0±0.2 degree C. The concentration of the solutions was mM order Fisher accumet model 525 digital pH/ion because solubility of acid form EDTA was to meter equipped with Metrohm combination that extent. electrode (glass electrode and Ag/AgCl reference (c) Potassium Nitrate solution. Reagent grade electrode) was used to measure the pH of of potassium nitrate was obtained from Wako solution to 0.001 digit. Pure Chemical Company. It was dried for 5 pH meter was calibrated with standard nitric hours at about 100 degree C and used without acid solutions which were conformed against further purification. standard potassium hydroxide solution. Ionic (d) Copper and Zinc Nitrate Stock solution.